The present invention relates to a cartridge for protecting an optical recording media accommodated therein.
Generally, the cartridge for protecting the optical recording media such as an MO (magneto-optic disc) has an opening from which the optical recording media is exposed and a shutter which covers the opening while the cartridge is detached from an optical disc drive. Since the opening is covered by the shutter, the MO in the cartridge can be protected against dust.
Further, the cartridge has a shutter lock mechanism which keeps the shutter closed while the cartridge is detached from the optical disc drive and a shutter release mechanism which release the shutter when the cartridge is inserted into the optical disc drive.
FIG. 9 shows a certain type of a conventional known cartridge 101 for a magneto-optic disc 109. As shown in FIG. 9, the cartridge 101 has a case 102, a shutter 103, a reception member 104 attached to the shutter 103 by screws, a lock arm 105 rotatably attached to the case 102, a torsion spring 107, and the magneto-optic disc 109 accommodated in the case 102. The case 102 has an opening 102a from which the disc 109 is exposed while the cartridge 101 is inserted in an optical disc drive (not shown). The shutter 103 is slidably attached to the case 102 and covers the opening 102a while the cartridge 101 is not used, i.e., while the cartridge is detached from the optical disc drive.
While the cartridge 101 is attached to the optical disc drive, a head provided in the optical disc drive is driven to record/reproduce information to/from the magneto-optic disc 109 through the opening 102a. 
In a situation shown in FIG. 9, i.e., while the cartridge 101 is not used, the shutter 103 is locked by engagement of the lock arm 105 and the reception member 104.
The lock arm 105 has an arm portion 105a, a hook portion 105b provided at one end of the arm portion 105a, and a hole 105c formed on the other end of the arm portion 105a. As shown in FIG. 9, a shaft 102b is formed on an inside wall of the case 102. The lock arm 105 is rotatably attached to the shaft 102b at the hole 105c formed on the other end of the arm portion 105a. 
The torsion spring 107 is attached to a shaft 102c formed on the inside wall of the case 102. One end of the torsion spring 107 contacts with the arm portion 105a, and the other end of the torsion spring 107 contacts with an inside wall of the case 102. Since the torsion spring 107 pushes the lock arm 105 upward on the FIG. 9, the hook portion 105b engages with the reception member 104. Consequently, the shutter 103 is kept closed while the cartridge 101 is not used.
Although the above described configuration of the cartridge 101 enables the shutter 103 to be kept closed while the cartridge 101 is detached from the optical disc drive, the conventional cartridge 101 has a problem that the shutter 103 is relatively easily opened by pushing the lock arm 105 using a pin through an opening 102e. The opening 102e is essential to mechanically release the shutter 103 when the cartridge 101 is attached to the optical disc drive.